The innate and adaptive immune systems are irrevocably linked and both play primary roles in the induction and/or prevention of infections, including periodontal disease. Critical to the initiation of innate and adaptive immune responses to microbial antigens is the participation of Toll-like receptors (TLRs), a family of patternrecognition receptors (PRRs) that detect conserved molecular products of microorganisms. We propose that the immune regulation exerted by the innate immune system upon its interaction with virulence antigens is the basis for the development of therapies geared to manipulate the effector immune response to the advantage and protection of the host. The fundamental hypothesis of our studies is that each microbial antigen is unique in its initial interaction with the host, thus resulting in differences in receptor recognition, activation of signaling pathways and cellular responses. In this regard, we have shown differences in the adaptive immune responses to the hemagglutinin/adhesin virulence antigens Kgp-HArep and HagB derived from Porphyromonas ginigivalis, which suggest that their interactions with the innate immune system differ. We plan to focus our investigations on the TLRs and on dendritic cells since these antigen-presenting cells have the exquisite property of activating naive T cells and thus are critically involved in innate and adaptive responses. In addition, our investigations will pursue an understanding of the ensuing adaptive immune response. Therefore, the aims of this proposal are (1) to determine the role of TLRs in the innate and adaptive response to Kgp-HArep and HagB stimulation; (2) to determine if innate and effector cell responses to Kgp-HArep and HagB require lipid rafts and how the induction of a specific effector response or the use of a certain TLR affects the particular recruitment and concentration of signaling molecules into lipid rafts; and (3) to determine the role of CD25+CD4+ Treg cells in immune responses to Kgp-HArep and HagB and in P. gingivalis infection. It is anticipated that these studies will lead to an understanding of the cellular events that occur when host cells encounter the virulence antigens HArep and HagB, and will provide 1) insight into their role in pathogenesis/immunity and 2) relevant information for the development of vaccines or therapies that will specifically protect or ameliorate infections by the pathogen Porphyromonas gingivalis.